In the field of magnetic field production, it is well known to generate an intense magnetic field by “magnets” constituted by one or more coils through which an intense electric current passes, said coils being cooled.
Said coils are generally constituted by cylindrical tubes made of conductive or superconducting material and cut out along an overall helicoidal cut-out line, at constant pitch or not, to form turns.
These coils for intense fields are currently almost exclusively used in intense magnetic field laboratories and could be of use for example in NMR machines, as per the acronym “Nuclear Magnetic Resonance” for the imaging via magnetic resonance.
These NMR machines usually have a structure of the tunnel type with a central space reserved for the patient and an annular structure which integrates both means for creating in the central observation space a homogeneous and intense main magnetic field, and radiofrequency excitation means and radiofrequency processing means for signals reemitted by the body of the patient placed in the central observation space, in response to the excitation sequences. To differentiate the radiofrequency signals sent in response and create an image, these machines also comprise coils known as gradient coils to superpose on the intense homogeneous field additional magnetic fields, the value of which depends on the spatial coordinates of their place of application.
Such an NMR machine is described for example in French patent application FR 2 892 524.
Gradient coils of magnetic fields or those generating an intense magnetic field are subjected to intense electromagnetic forces which cause mechanical stresses leading to deformation of the turns of the coil. Deformation of the turns can cause a lack of reliability of the machine and/or non-homogeneity of the magnetic field detrimental to high-quality imaging production.
Documents U.S. Pat. No. 2,592,802, EP 0 146 494 and U.S. Pat. No. 3,466,743 which describe induction coils are also known.
Document U.S. Pat. No. 2,592,802 describes an induction coil comprising a tube made from conductive material and cut out along several overall helicoidal cut-out lines to form turns which are separated by a vertical portion ensuring separation between the turns. Said separation portion is cut out to form a pair of spacing members on either side of a cylindrical hole in which is advantageously inserted a rod made of insulating material.
Document EP 0 146 494 describes an induction coil comprising incomplete annular cut-outs made in a cylindrical tube, said incomplete annular cut-outs being connected by two vertical cut-outs. This type of induction coil is intended to displace spacers in nuclear reactors and is not intended to receive high-intensity currents to form intense fields.
Document U.S. Pat. No. 3,466,743 describes a coil comprising a tube made of conductive material and cut out along an overall helicoidal cut-out line to form turns, said turns passing through holes initially made along the tube, the cut-out line being filled with insulating material to prevent any deformation when very high-intensity currents pass through the coil.
None of the coils described in these documents is intended to form fields known as intense fields and does not absorb stresses caused by electromagnetic forces on the turns of the coils.